Claws Mail version 3.14.0-39-g986e6f-dirty
Windows 10 PRO, ver 1607, OS Build 14393.187
64 bit machine

I have been experiencing crashes with this version of claws-mail ever since I loaded the vcalendar.dll module. Claws-mail would crash sometimes immediately when loading; other times hours later. Sometimes I would be working with it and other times I would be away from the PC. I finally ran claws-mail under gdb and this is what got back:

Microsoft Windows [Version 10.0.14393]
(c) 2016 Microsoft Corporation. All rights reserved.

C:\Users\Gerard>"C:\Users\Gerard\Downloads\New Folder\gdb.exe" "C:\Program Files\Claws Mail\claws-mail.exe"
GNU gdb (GDB) 7.7.50.20140303-cvs
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This binary was built by Equation Solution <http://www.Equation.com>...
Reading symbols from C:\Program Files\Claws Mail\claws-mail.exe...(no debugging symbols found)...done.
(gdb) run
Starting program: C:\Program Files\Claws Mail\claws-mail.exe
[New Thread 15556.0xc08]
[New Thread 15556.0x4548]
[New Thread 15556.0x4a18]
[New Thread 15556.0x4614]
[New Thread 15556.0x2184]
[New Thread 15556.0x4148]
[New Thread 15556.0x3828]
[New Thread 15556.0x50c]
[New Thread 15556.0xe18]
[New Thread 15556.0x4bcc]
[New Thread 15556.0x4b00]

Program received signal SIGSEGV, Segmentation fault.
0x000000006f802dbb in vcalendar!icalvalue_isa_value () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
(gdb) bt full
#0  0x000000006f802dbb in vcalendar!icalvalue_isa_value () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#1  0x000000006f7f8195 in vcalendar!icalproperty_add_parameters () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#2  0x000000006f7edec7 in vcalendar!icalproperty_vanew_attendee () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#3  0x000000006f7c827e in vcalendar!vcal_manager_event_dump () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#4  0x000000006f7d6a54 in vcalendar!multisync_export () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#5  0x000000006f7d6c65 in vcalendar!vcal_meeting_export_calendar () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#6  0x000000006f7cb9cd in vcalendar!vcal_folder_export () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#7  0x000000006f7cf442 in vcalendar!vcal_get_events_list () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#8  0x0000000000440515 in folder_item_scan_full ()
No symbol table info available.
#9  0x000000006f7c5bc8 in vcalendar_init () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#10 0x000000006f7c14e7 in vcalendar!plugin_init () from C:\Program Files\Claws Mail\lib\claws-mail\plugins\vcalendar.dll
No symbol table info available.
#11 0x00000000005771d3 in plugin_load ()
No symbol table info available.
#12 0x0000000000576f38 in plugin_load ()
No symbol table info available.
#13 0x000000000057791b in plugin_load_all ()
No symbol table info available.
#14 0x00000000005e127e in main ()
No symbol table info available.
(gdb) quit
A debugging session is active.

        Inferior 1 [process 15556] will be killed.

Quit anyway? (y or n) y

I had to kill “gdb” in order to shut claws-mail down. I then restarted claws-mail. As usual after this type of crash, it would immediately crash again. I had to restart it many times before it would finally stay loaded. I have discovered that if I quickly “X” out of the program immediately as it starts and they hit "quit" in the pop-up window, claws-mail will sometimes stay running or at least start up normally the next time. Very strange to say the least.

I have now unloaded the “vcalendar.dll” module and all is well. The system has been running for 24 hours without a problem. I believe that there is an inherent problem with the vcalendar.dll module and Windows 10 PRO.